Infrared detector cooler



Dec. l0, 11968 N. D. L lsroN INFRARED DETECTOR COOLER Filed July 51, l967` Heem?? United States Patent Otice 3,415,078 Patented Dec. 10, 1968 t 3,415,078 INFRARED DETECTOR COOLER Novell D. Liston, Pomona, Calif., assigner to General Dynamics Corporation, a corporation of Delaware Filed July 31, 1967, Ser. No. 657,147 7 Claims. (Cl. 62-514) ABSTRACT OF THE DISCLOSURE The disclosure is directed to an infrared detect-or cooling arrangement wherein the cryostat assembly includes an exhaust tube which extends through a precooling chamber into a detector chamber with cooldown gas and stabilization gas tubes closely wrapped about the exhaust tube and which also extend into the detector chamber. The cryostat assembly is precooled yby application of a precoolant gas which flows over the gas inlet tube, stabilization tube, and exhaust tube in the precooling chamber. The cryostat or cooldown gas is then applied to the inlet tube and expands in the detector chamber to rapidly drop the temperature thereof and discharges through the exhaust tube where it additionally precools the gas in the inlet and stabilization tubes. At some predetermined time preselected gas is applied through the stabilization tube and expands in the detector chamber to maintain or stabilize the temperature therein and discharges through the exhaust tube.

Background of the invention This invention relates to Joule-Thomson effect cooling apparatus and more particularly to a Joule-Thomson effect cooling system which utilizes a precooling chamber providing fast initial cool-down to a reduced temperature and subsequent maintenance of such temperature by the use of preselected coolants.

Prior efforts have been directed to various systems for cooling apparatus such as infrared detectors. U.S. Patent 2,991,633 exemplifies prior art approaches for producing rapid cooldown and subsequent maintenance utilizing the same coolant discharged through different size tubes. None of the known prior art efforts have, as in the present invention, utilized a precooling chamber in combination with a stabilization coolant of a type different than that used as the rapid cooldown coolant.

Summary of the invention Therefore, it is an object of this invention to provide an improved Joule-Thomson effect cooling system.

Another object of the invention is to provide a Joule- Thomson effect cooling system which utilizes a precooling arrangement.

Another object of the invention is to provide a Joule- Thomson effect cooling system which has fast initial cooldown and temperature stabilization capabilities.

Another object of the invention is to provide an infrared detector cooler assembly which utilizes precooling and temperature stabilization.

Another object of the invention is to provide an infrared detector-cooler which utilizes precooling, rapid cooldown, and temperature stabilization fluids.

Other objects of the invention will become readily apparent from the following description and accompanying drawing wherein:

Brief description of drawing The single figure is a partial cross-sectional view illustrating an embodiment of the invention.

Description of the embodiment The detector cooling system of this invention operates on a basic thermodynamic process known as the open Joule-Thomson expansion, wherein the expansion of high pressure gaseous refrigerants through a porous plug or throttling valve at constant enthalpy results in a reduction in temperature of the gas. Thus, careful selection of refrigerants will provide cryogenic temperatures required for quick cooldown.

The temperature stabilized, rapid cooldown, miniature infrared (IR) detector system, as illustrated in the drawing, consists of two major components which are the precooling assembly 10 and detector assembly 11. The precooling assembly 10 includes a housing 12 defining an open end chamber 13. A precoolant gas inlet tube or conduit 14 is connected through housing 12 with chamber 13 and is adapted to supply high pressure, ambient temperature pre-coolant gas to chamber 13 from a source (not shown). Within chamber 13, a cooldown refrigerant inlet tube 15 and a stabilization refrigerant inlet tube 16 are wound around an exhaust tube 17 in the form of a helix which serves as a heat exchanger coil. Detector assembly 11 includes a housing 12 which, as illustrated is a continuation of housing 12, but may be separate housing sections secured together. Housing 12 defines an open end chamber 18. Secured to housing 12 and sealing the outer end of chamber 18 is an IR detector unit 19 as known in the art and which is adapted to be cooled down by the inventive cooling system. Exhaust tube 17 extends into housing 12' and terminates adjacent the outer end of chamber 18 and IR detector unit 19. Refrigerant leakage between 12' and tube 17 is prevented tiy seal means 20, such as an O-ring. The terminals ends 21 and 22 of cooldown tube 15 and stabilization tube 16, respectively, extend through chamber 18 and terminate a preselected distance from the IR detector unit 19. Housing 12 is provided with ange portion 23 defining an exhaust port 24 and a ange portion 25, while housing section 12 is provided with a flange portion 26 which abuts flange 25.

In operation, high pressure, ambient temperature refrigerant simultaneously enters the precoolant gas inlet 14 and cooldown gas inlet 15. The precoolant gas enters the precooling chamber 13 at the forward end and expands and flows over the coils of tubes 15 and 16 toward the exhaust port 24 of housing 12 thus cooling the fluid in rapid cooldown tubing 15 due to the expansion of the precoolant gas in chamber 13. The refrigerant in the `rapid cooldown gas tube 15 flows through the helical windings thereof where it is cooled by the expanding precoolant gas, and passes on through the terminal end 21 thereof in detector assembly 11 and discharges against and expands as a two phase mixture consisting of liquid droplets in a saturated vapor at the detector post of the IR detector unit 19 producing rapid detector cooling, and then passes out through the exhaust tube 17, the exhausting fluid passing through exhaust tube 17 causing further cooling of the fluid flowing in the terminal end 21 of cooldown tubing 15. At some predetermined time, flow in the rapid cooldown tubing 15 stops and a second refrigerant begins owing in the stabilization Atubing 15 which is cooled by the expanding gas as described above and expands at the post of detector unit 19- producing a stabilized temperature for maximum detector sensitivity.

l By way of example only, high pressure, ambient temperature argon refrigerant enters the rapid cooldown gas linlet tube 15 and 1000 p.s.i.g., ambient temperature carbon dioxide enters the precooled gas inlet tube 14 simultaneously. The carbon dioxide expands in the precooling chamber 13 resulting in a low temperatureow of gas across the cooling coil. The argon flowing inside the `cryostat or cooldown coil 15 is cooled while remaining at high pressure. The cooled, high pressure argon then expands at the detector post as a two phase mixture consisting of liquid droplets in a saturated vapor. This two phase mixture will provide the necessary low temperature and high heat transfer coefficient required lto reduce an optimized detector configuration temperature to 100 C. in one second. Since detector sensitivity is a function of temperature, the detector temperature should be lowered to 100 C. and be stabilized at 100 C. quickly. As pointed out above, the cooldown -refrigerant (argon) fiow is stopped and a ow of Freon 14/23 mixture with a 100 C. boiling temperature will begin in the stabilization cryostat inlet tube 16. This Freon 14/ 23 mixture will expand at the post of detector unit 19 producing a stabilized 100 C. temperature.

Tests have shown that by utilizing an infrared detector cooling system as described above, a capability of cooling an optimized detector from 21 C. to 100 C. in one second and immediately stabilizing at 100 C. is provided, thus providing maximum detector sensitivity.

While the inventive cooling system has been described with respect to and is particularly adapted for use in cooling infrared detector units, it is within the scope of this invention to utilize this concept in various applications which require rapid cooldown and temperature stabilization.

Although a particular embodiment of the invention has been illustrated and described, modifications and changes will become apparent to those skilled in the art, and it is intended to cover in the appended claims all such modifications and changes as come within the true spirit and scope of the invention.

What I claim is:

1. A Joule-Thomson effect' cooling device comprising: a housing defining a chamber means extending therethrough, a fiuid exhaust tube operatively positioned in said housing chamber means, a pair of tubes coiled around at least a portion of said exhaust tube and terminating at one end adjacent one end of said exhaust tube, one of said pair of tubes being adapted to supply cooldown refrigerant to an associated point of use adjacent the said one end of said exhaust tube, the other of said pair of tubes being adapted to supply temperature stabilization refrigerant to the associated point of use, tubing means operatively connected to said chamber and adapted for supplying precoolant fluid thereto.

2. The cooling device `defined in claim 1, wherein the cooldown refrigerant, the temperature. stabilizationfrefrigerant, and the precoolant fluid are each composed of different fiuids.

3. The cooling device defined in claim 2, wherein the cooldown refrigerant is argon, the temperature stabilization refrigerant is a Freon 14/23 mixture, and the precoolant uid is carbon dioxide.

4. The cooling device defined in claim 1, in combination with an infrared detector u-nit, said infrared detector unit being positioned adjacent said one end of said exhaust tube, and adjacent the said terminal one end of each of said pair of tubes, whereby the detector unit is rapidly cooled down to a preselected temperature and maintained at said temperature for a predtermined time.

5. The combination defined in claim 4, wherein the cooldown refrigerant is argon, the temperature stabilization refrigerant is a Freon 14/ 23 mixture, and the precoolant fluid is carbon dioxide.

6. The device defined in claim 1, wherein said housing is provided with a pair of flange portions, one of said tiange portions being provided with an exhaust opening of a cross-section larger than said chamber means crosssection; said chamber means being composed of a pair of sections of different cross-section, the larger cross-sectional section of said chamber means defining a precooling chamber and the smaller cross-sectional section detning a cooling chamber, said coiled portion of said pair of tubes being located in said precooling chamber, said precoolant fluid tubing means being operatively connected with said precooling chamber, said one end of said exhaust tube and said terminal ends of said pair of tubes being located in said cooling chamber; and sealing means positioned between said precooling chamber and said cooling chamber and about said exhaust tube and said pair of tubes to prevent tiuid exhausting from said terminal ends of said pair of tubes from passing externally of said exhaust tube from said cooling chamber to said precooling chamber.

l 7. The device defined in claim 6, wherein said precoolant fluid tubing means is connected at the end of said precooling chamber adjacent said cooling chamber.

References Cited UNITED STATES PATENTS l 3,095,711 7/1963 Wurtz 62-514 3,326,015 6/1967 Webster 62--514 3,364,697 1/1968 Garrett 62-514 MEYER PERLIN, Primary Examiner. 

